As the novel opens, Adam is a rebellious teenager who think his father hates him. Even as the battle of Lexington is beginning, Adam behaves like a child. The reality of war hasn't hit him yet, and he brings with him only his birding gun, which shoots pellets, not real bullets.
During the two days of battle, however, Adam quickly grows up. First, he understands that his father cares about him. As he says later to Cousin Simmons:
I was so happy last night ... When we walked across to the common, he put his arm on my shoulders. I felt that he truly loved me. That was the first time I ever felt it.
However, Adam also sees his father killed, and realizes it is up to him to take care of his brother Levi. He recognizes that death is real, understanding that, as he puts it:
I had parted with childhood and boyhood forever.
As he enters his house after the battle, he says that he remembered:
childhood and clung to both, but hopelessly. By the time I entered my house, I had surrendered them.
At home, people treat him differently. Levi looks at him with hero worship. His mother expects him to take on the mantle of head of household, and he intends to do so. Even his Granny looks to him as someone she will have to depend on.
Adam started the Battle of Lexington not accepting the reality of a war with the British, but now he does. He also knows he will eventually marry Ruth.
War and his father's death thrust maturity onto Adam, and he rises to occasion. He might not have wanted to grow up so fast, but the chaos of battle teaches him that he can be a grown up without having to know everything. He recognizes that although only 15, he has what it takes to assume adult responsibilities.